Although significant advances have been made in treating agoraphobia over the past 30 years, current exposure-based methods achieve incomplete results, with about 30% of agoraphobics showing little or no benefit, and the majority leaving treatment with at least some residual areas of disability that do not later improve. The goals of the proposal research are to increase understanding of the treatment of agoraphobia, specifically (a) to elucidate the role of the therapist in conducting in vivo exposure treatments, and in particular to determine whether the therapist can achieve better results by actively assisting agoraphobics during exposure (Guided Mastery treatment) than by simply encouraging them to expose themselves to phobic stimuli for prolonged periods (Flooding treatment); (b) to examine several widely proposed emotional and cognitive mechanisms of therapeutic change in agoraphobic behavior, including anxiety, panic attacks, anticipated anxiety, anticipated panic, perceived danger, and perceived self-efficacy; (c) to examine, patterning, and mechanisms of generalized change to untreated phobias following exposure; (d) to evaluate the role of self-exposure homework and spouse/partner assistance in promoting generalization and maintenance of change, and (e) to measure therapeutic effects and psychological mechanisms by precise behavioral tests conducted in the natural community environment. A series of five experiments will be conducted with three successive waves of agoraphobic subjects. Studies 1 and 2 with the first wave of subjects will consist of highly focussed tests of prototypical Mastery and Flooding treatments given without exposure homework. Studies 3 and 4 with the second wave of subjects will evaluate Guided Mastery and Flooding treatments given in combination with exposure homework. Study 5 in the third we will examine the possible added contribution of spouse/partner exposure assistance. Studies 1-4 will evaluate generalization by initially treating each subject for only some phobias, while measuring the changes in both the treated and untreated phobias.